1. Field of the Invention
The invention relates to the field of fusing optical fibers and more particularly to a furnace for performing such fusion.
2. Description of the Prior Art
Coupling of optical signals from one optical fiber to other optical fibers is accomplished in an optical fiber coupler. These couplers comprise an input fiber from which the light is coupled to one or more other fibers. To accomplish this coupling, the buffer material around the cladding is removed over equal distances for each fiber and the exposed sections are fused to form the coupling region. Such fusion has been performed in the prior art by clamping the fibers together and applying heat directly to the aligned exposed sections with a hand held torch. This method requires a highly skilled operator, for the torch must be applied in a very small region, uniformly for a precise time interval, necessitating a great degree of eye-hand coordination and fusion completion judgement. Taper angles which determine the degree of coupling and the coupling efficiency are difficult to control, since the fibers must be drawn while the heat is being applied. Further, the fibers have extremely small cross-sectional areas and are subject to breakage caused by wind turbulence created by the torch.
Some of the difficulties encountered with the hand torch method are alleviated by placing the fibers in a heat conducting tube and applying the torch to the outer surface of the tube. In this method it is difficult to concentrate the heat to the desired coupling region and claddings may be removed or fused in areas where such removal and fusion is not desired.
Another method of the prior art for fusing the optical fibers in the coupling region utilizes a ringed heating coil surrounding the coupling region through which an electric current is passed. As with the heated tube process, heat concentration is difficult to achieve and the temperature in the coupling region difficult to control.